The general interpretation of tables of numerical or statistical data is a problem, especially when large amounts of information are involved. An early solution was the invention of simple two dimensional graphing techniques. More sophisticated applications have since evolved which require the simultaneous viewing of data varying in three or more independent dimensions. This is particularly true for demographic data, which must overlay some type of map. Typically, three dimensional solutions use overlays of various shades of gray, or forms of crosshatching, but these methods have drawbacks. One drawback is a tendency to mask the underlying chart. Another is such methods have not been easy to integrate with computer processing.
In recent years, computing costs, as well as color reproduction costs have been coming down, which has created the need for an improved method of generating artwork for color graphs of this type, termed "charts" herein. Furthermore, since hue, intensity, and saturation may all be independently changed, a fourth and even fifth dimension is now quite possible using color.
Numerical data is now, for the most part, processed by computers, and thus it is quite logical to use them directly in the preparation of charts. Indeed, graphical output devices for computers have existed for many years for just this purpose. Equipment tends to fall into one of two catagories, medium to high resolution "hard copy" plotters, and low resolution video display systems, often with a camera attached. The highest resolution devices are photoplotters, which draw on lithographic film with light. These are used for line drawings for maps and in the electronics industry, and have been used to draw charts using solid lines. Prior to the subject invention, photoplotters had limited application in the generation of color charts having more than one color per sheet of exposed film. Very limited color output from computers has also been available using pen-plotters, which draw with liquid ink or ball-point pens. Like photoplotting, charts produced this way can only contain a few colors (one per pen), and then only solid or dashed lines. Some video display systems can be used to generate color charts under computer control, but generally suffer from a limited range of colors, and low resolution.